Picheo comes from the English verb 'to pitch' from baseball, but it's a fantastic example of Spanglish slang!
In Puerto Rico and other parts of the Caribbean, 'pichear' means to ignore someone or to dodge a situation. In the song, Bad Bunny brags, 'Yo siempre picheo, denme el Cy Young' (I always ignore them, give me the Cy Young award), cleverly comparing his skill at ignoring haters to being the best pitcher in baseball.
This song is Bad Bunny at his most confident, and it's impossible not to feel it too. The whole message is a powerful declaration of self-belief, starting with the hook: "¿Quién dijo que no? Que no puedo / Yo hago lo que me dé la gana" (Who said no? That I can't? / I do whatever I want). He's not just talking about himself, though. He immediately follows up the line "El mundo es mío" (The world is mine) with "El mundo es tuyo" (The world is yours), turning his personal anthem into an invitation for everyone to feel the same way.
He spends the rest of the song listing exactly why he feels this way, and it's a masterclass in bragging. He claims his legacy is eternal, saying God told him he'll last forever, unlike what salsa legend Héctor Lavoe sang about everything having an end. He even boasts that if boxing champion Floyd Mayweather challenged him, "también lo derroto" (I'd defeat him too). It's over-the-top, fun, and completely infectious. He's telling you he's on top of the world and wants you to join him there.